This application claims the priority of German Application No. 100 37 575.8, filed Aug. 2, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an electronic control unit for automatically activating a parking brake and a method for preventing the automatic activation of the parking brake in motor vehicles.
From German patent document DE 196 25 019 A1, for example, an electronic control unit is known in the form of a transmission control device, which in addition to other vehicle functions is used for automatically activating a parking brake. The parking brake is automatically activated independent of at least one specified operating mode of a motor vehicle, which is started up with a mechanical ignition key. Such an operating state can include e.g. falling short of a certain vehicle speed threshold, the position of the ignition key in the lock and/or the state of the vehicle door (open/closed). However, at the latest, the parking brake is activated upon removing the ignition key from the lock.
In the future, key-less access and/or driving authorization systems are used increasingly in order to start motor vehicles. Such a system is known for example from the electronic authorization verification device from German patent documents DE 198 01 064 A1 and DE 198 23 707 A1. Here, wireless code transmission takes place to establish the access and driving authorization. A mechanical ignition key is only provided as a redundant feature. The vehicle is then started and turned off with a rotary switch with simultaneous verification of the authorization through the authorization verification device. After shutting the vehicle off, no mechanical key therefore has to be pulled out of the ignition.
Nevertheless, automatic activation of a parking brake with a removed key, wherein an electronic authorization verification device should be considered equal to a conventional key system from a functional point of view, is required by law in some countries. For safety reasons, on vehicles without mechanical keys, the parking brake is therefore automatically activated independently of a key position in dependence of at least one other operating parameter or operating state. Operating parameters or signals that indicate the user has left the vehicle in particular are evaluated, such as an open driver's door (can be interrogated with a switch in the door) or an empty driver's seat (can be recognized with seat occupation sensors). In some situations, however, this is associated with undesirable restrictions. For example, pushing a “stalled” vehicle is no longer possible.
The goal of the invention is to prevent undesirable restrictions associated with an automatic parking brake, without impairing safety.
This goal is achieved by an electronic control unit and method for automatically activating a parking brake in dependence of at least one specified operating parameter or operating mode of a motor vehicle, which can be started without a mechanical key. Means are provided for arbitrarily preventing the automatic activation of the parking brake. Beneficial embodiments of the invention are the objects of the dependent patent claims and are described herein.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.